Rates and equilibrium

Question 1

What is the rate of a chemical reaction in terms of reactants?

Answer 1

How quickly the reactants in a reaction are used up

Question 2

What is the rate of a chemical reaction in terms of products?

Answer 2

How quickly the products in a reaction are formed

Question 3

What is the formula for a mean rate of reaction in terms of reactants?

Answer 3

quantity of reactant used/time taken

Question 4

What is the formula for a mean rate of reaction in terms of products?

Answer 4

quantity of reactant product formed/time taken

Question 5

How can you measure the quantity of a reactant or product?

Answer 5

In grams or in cm³

Question 6

What are the two possible units for rate of reaction?

Answer 6

g/s or cm³/s (where s is seconds)

Question 7

How could you measure the rate of a reaction from a graph?

Answer 7

Draw a tangent to the curve and calculate the gradient.

Question 8

What is “collision theory”?

Answer 8

The theory that chemical reactions only occur when particles collide with sufficient energy

Question 9

What factors can affect the rate of a reaction?

Answer 9

Temperature, surface area of a solid, concentration or reactants in solution, pressure of gases

Question 10

State the effect of increasing the surface area on the rate of a reaction

Answer 10

Increases the rate

Question 11

Explain why increasing the surface area increases the rate of a reaction

Answer 11

More particles are available to collide, there are therefore more frequent collisions between reactants.

Question 12

State the effect of increasing the concentration on the rate of reaction

Answer 12

Increases

Question 13

Explain why increasing the concentration increases the rate of reaction

Answer 13

More concentrated means more particles in solution, therefore more frequent collisions between reactants.

Question 14

State the effect on increasing the pressure of a gas on the rate of reaction

Answer 14

Increases

Question 15

Explain why increasing the pressure of a gas increases the rate of a reaction

Answer 15

Less space for the particles to move around in, therefore more frequent collisions

Question 16

State the effect of increasing the temperature on the rate of reaction

Answer 16

Increases

Question 17

What is the activation energy?

Answer 17

The amount of energy a particle needs before it will be able to react when it collides with another particle

Question 18

Explain why increasing the temperature increases the rate of reaction

Answer 18

Increases the speed at which particles move therefore more frequent collisions. Increases the number of particles which have the activation energy therefore more collisions result in a reaction.

Question 19

What is a catalyst?

Answer 19

Something which changes the rate of a reaction but is not used up in that reaction

Question 20

How do catalysts speed up reactions?

Answer 20

They provide another route for the reaction to take place which has a lower activation energy.

Question 21

What is a reversible reaction?

Answer 21

A reaction which can go from reactants to products but also from products to reactants

Question 22

What chemical symbol represents a reversible reaction?

Answer 22

⇌

Question 23

If a reaction is exothermic in the forward direction what will it be in the reverse direction?

Answer 23

Endothermic

Question 24

Two reactants require 30kJ to turn into products. What energy transfer is involved when the products turn into reactants?

Answer 24

30kJ is released

Question 25

What is equilibrium?

Answer 25

The point in a reversible reaction when the forward and reverse reactions are occurring at the same rate

Question 26

How is the amount of reactant changing at equilibrium?

Answer 26

It is not changing

Question 27

How is the amount of product changing at equilibrium?

Answer 27

It is not changing

Question 28

What is Le Chatelier’s principle?

Answer 28

When a reaction at equilibrium is changed, it will seek to counteract that change

Question 29

A reaction is exothermic in the forward direction. What will occur if the temperature is increased?

Answer 29

The backward reaction will increase as it is endothermic and will reduce the temperature

Question 30

A reaction is at equilibrium when some product is removed. What will occur?

Answer 30

The forward reaction will increase as that will increase the amount of product

Question 31

The reaction below is at equilibrium. What will occur when the pressure is increased? 2H₂(g) + O₂(g) ⇌ 2H₂O(g)

Answer 31

The forward reaction will increase as there are fewer molecules on the right. This will reduce the total number of molecules and therefore the pressure.